Apparatus and method for the processing of solid materials, including hard tissues

ABSTRACT

A method and apparatus are provided for processing solid materials in general, and of dental material in particular, which involves applying radiation from a laser or other suitable pulsed radiation source to process and to preferably ablate the material in a region of processing thereof. Particles of ablation are generated by the radiation from the area of processing and/or other source(s) which are directed to the area of processing to further process the material. Particles adhering to a tip through which the radiation is applied, to a reflector or other surfaces adjacent the region of processing at the end of each radiation pulse may be ablated and accelerated back to the region of processing by the next pulse. Ablation particles may also be obtained from the ablation of the tip, from a strip of material through which radiation passes before reaching the region of processing or from other sources. Mechanism may also be provided for cooling the surface of the material in the region of processing between radiation pulses and/or during such pulses and/or for facilitating removal of particles in the area between the chip and the region of processing between radiation pulses.

FIELD OF THE INVENTION

The invention concerns methods and apparatus for the processing of solidmaterials, including hard tissues, metals, ceramics, crystals, glass,certain plastics, etc. and uses thereof in dentistry, surgery,orthopedics and other material processing applications.

BACKGROUND OF THE INVENTION

Laser radiation is widely used for the processing of hard materials:drilling, cutting, modification of properties and other operations. Themechanism for destruction of hard materials under the influence of laserradiation involves the absorption of laser energy, which results inheating, melting and evaporation of the materials. Other mechanismsinvolve absorption of radiation by strongly absorptive materials(chromophores), their heating and the breaking of the material becauseof pressure around the absorptive materials. The process of laserdestruction of materials under the influence of short pulses (generallypulses shorter than the thermal relaxation time of the target) issometimes called laser ablation. In order to reach the maximumefficiency of material removal, the wavelength of the laser radiation isselected to be within the range of maximum absorption for the absorptivematerial. Depending on the properties of the material, the optimumparameters of laser radiation are selected. These parameters include thewavelength, the pulse duration, the diameter of laser beam spot, and theenergy or power. Laser destruction of hard materials has a lot ofadvantages; however, in many cases it is slower than drilling or othermechanical methods of processing.

Russian certificate of invention USSR N 1593669, published Sep. 23,1990, discusses the removal of hard tooth tissues by radiation with 2.94μm wavelength (Er:YAG laser), with pulse duration of 100-500 μs and withenergy of 0.5-1 J. U.S. Pat. No. 5,257,935 issued Oct. 2, 1993 proposesa laser with a wavelength within the range 1.5-3.5 μm, in particular2.94 μm, for the same objective. The radiation in this device isdelivered from the laser to the processing zone using an optical fiberconnected to a tip in contact with a tooth surface. The disadvantage ofthis method and apparatus is that the speed of material removal isslower than for high-speed drills. Its use therefore results in anincrease in procedure duration. However, the laser procedure is in mostcases painless and does not require anesthesia. The laser processing isalso less traumatic.

In the apparatus and method disclosed in the U.S. Pat. No. 5,409,376,issued Apr. 25, 1995, mechanical drilling is combined with laserdrilling in order to increase the speed of processing. However, thisincreases the price of both the treatment process and the drillingapparatus. Further, when used for the processing of dental tissues, itresults in the loss of the main advantages of laser processing—absenceof pain and low danger of trauma.

A major disadvantage of the techniques discussed above is insufficientutilization of the laser energy. This is due to the fact that asignificant part of the laser pulse energy absorbed by the processedmaterial is transformed to mechanical energy of particles leaving thezone of processing, this energy being uselessly spent in heating theenvironment. Similar issues can arise when a laser is used to ablatesolid materials other than dental tissue.

SUMMARY OF THE INVENTION

In accordance with the above, this invention, in accordance with a firstaspect thereof, provides a method of processing a solid material whichincludes exposing the material to pulsed radiation with an energy abovean ablation threshold for the material; and returning or otherwisedirecting particles of ablated material to a region of processing of thematerial to further influence material processing. Some of the particlesof ablated material will be deposited on a surface adjacent the regionof processing, the method including returning these deposited particleto the region of processing in response to the next radiation pulse tofurther process the material. While the region of processing is thesource of the particles of ablated material for a preferred embodiment,other sources of particles may also exist, either in addition to orinstead of the preferred source, which particles can be delivered to theregion of processing for the further processing of the material.Potential sources for such added material include a tip through whichradiation is delivered, reflectors surrounding the tip and/or anadditional piece of material positioned between the radiation source andthe region of processing which may be ablated by radiation passingtherethrough to produce accelerated particles. For a preferredembodiment, the material being processed is a dental material, forexample dental enamel, dentin, bone, stain, filling material, cementumand the like. For such embodiments, the pulsed radiation is preferablyfrom a laser with a wavelength within one of the bands 1.9-2.1 μm,2.65-3.5 μm, 5.6-7.5 μm, and 8.5-11 μm; a duration of 0.0001-10000 μs(preferably 1-500 μs); and an energy density of 0.5-500 J/cm². Themethod may also include cooling the region of processing of the materialand/or removing particles from an area between a source of the pulsedradiation and the region of processing, these steps preferably beingperformed between pulses of the radiation for some embodiments. Foranother embodiment, air is first applied to the region of processing toclean at least the area. A light water spray or mist is then applied toboth cool the area and to be ablated, the laser or other radiationsource being fired during the applications of the mist. After the firingof the radiation source, the misting or a stronger water spray may beapplied to cool the region of processing. While the three stepsindicated above are preferably used together, for some embodiments, oneor more of these steps may be individually performed.

The invention also includes a device for processing a solid materialwhich includes a source of pulsed radiation and a system for deliveringradiation from the source through a tip to a region of processing, thetip including an end for delivering radiation to at least one particlesource, the radiation accelerating particles from the particle source,which particles are accelerated and/or reflected to a region ofprocessing on the surface of the solid material to influence theprocessing thereof. For preferred embodiments, the particle source isthe region of processing on the surface of the solid material, theradiation ablating the surface to create particles of ablationaccelerated away from the surface, at least some of these particlesbeing reflected back to the region of processing by at least one of thetip and a reflector surrounding the tip to further process the surface.The radiation and the reflected particles may impinge on substantiallythe same point in a region of processing or they may impinge ondifferent points in this region to increase the area being processed.

At the end of at least some radiation pulses, some particles of ablationmay adhere to the tip or other surfaces adjacent the area of processing,and these adhered particles may serve as an additional particle sourcefor a subsequent radiation pulse, the adhered particles being ablated bysuch radiation pulse so as to be accelerated toward the region ofprocessing. For some embodiments, the tip has an end facet shape tofunction as a reflector for the particles. At least a portion of the tipmay also be ablated by the radiation, the ablated portion of the tipbeing a source of particles for delivery to the region of processing. Aunit may also be positioned between the tip and the region of processingwhich unit is ablated by radiation applied thereto to produce particlesof ablation directed to the region of processing. A mechanism may beprovided for advancing the portion of the unit between the tip and theregion of processing as the unit is ablated. For preferred embodiments,the source of pulsed radiation is a pulsed laser.

The particles from the particle source are of a hardness which is atleast close to that of the material in the region of processing and ispreferably of a greater hardness. For preferred embodiments, the sourceof pulsed radiation is a pulsed laser.

A mechanism may also be provided for facilitating the removal ofparticles from an area between the tip and the area of processing,generally between radiation pulses. This mechanism may include amechanism for vibrating the tip, the vibrations being preferablysynchronized with the pulsed radiation to enhance particle delivery tothe region of processing and/or the removal of particles. The mechanismfor facilitating removal may alternatively include a mechanism forapplying to the area between the tip and the area of processing aliquid, a gas, and/or underpressure to facilitate the removal of theparticles. For certain embodiments, such delivery mechanism operates atleast primarily between pulses from the source of pulsed radiation.Liquid and/or gas applied between pulses may also function to cool thesurface of the area of processing. For another embodiment, air isapplied before a radiation pulse to clean at least the area ofprocessing, followed by a fine water spray or mist for at least coolingthe region of processing, the radiation pulse occurring during themisting. The radiation pulse preferably lags the misting by at least asufficient time for a thin water coating to form on the area ofprocessing. The misting or a stronger water spray is applied after theradiation pulse.

The tip, instead of being solid, may be either hollow or liquid filled.A hollow tip may be shaped to minimize entry of particles from theparticle source therein. The tip may also have an in facet cut at anangle to facilitate side processing of the material.

For preferred embodiments, the radiation is at a wavelengthpreferentially absorbed by the solid material. The radiation may alsohave a pulse duration which is of the same order or shorter than thethermal relaxation time of an absorbing fraction of the solid material.The distances between the end of the tip and a surface of the materialto be processed is preferably not more than a distance of flight of theparticles during which their speed decreases by a factor of 10.

The tip may be a dielectric waveguide with an end facet which is one offlat, elliptical and spherical. The tip may also include a microlens ormay include some other portion focusing the radiation at or below thesurface of the region of processing. A reflector may also be providedwhich surrounds the end of the tip and is shaped to direct the particlesto the region of processing and to control the dimensions of suchregion.

As indicated earlier, for preferred embodiments, the solid material is adental material such as dental enamel, dentine, bone, other dentaltissue, filling material, cementum or stain. For such embodiments, thesource of pulsed radiation is at a wavelength preferentially absorbed bysuch dental material. In particular, the source of pulsed radiation forsuch embodiments is preferably a pulsed laser. Examples of suitablepulsed lasers include Er:YAG with a wavelength of 2.94 μm, Er:YLF with awavelength in the 2.71-2.87 μm range, Er:YGG with a wavelength of2.7-2.8 μm, CTE:YAG with a wavelength in the 2.65-2.7 μm range,Ho:KGd(WO₄)₂ with a wavelength of 2.93 μm, and CO₂ with a wavelength inthe 9-11 μm range.

The foregoing other objects, features and advantages will be apparentfrom the following more particular description of preferred embodimentsas illustrated in the accompanying drawings, the same reference numeralbeing used for common elements in the various figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 are schematic diagrams of an experimental setup forthe destruction of a substance using the energy of ablation products andthe results of this processing respectively.

FIGS. 3a and 3 b are semi-schematic side views of a device for theprocessing of materials in accordance with the teachings of thisinvention, including a particle reflector located around an outputwaveguide end facet and an enlarged view of the tip of the device,respectively.

FIG. 4 is an enlarged view of a portion of FIG. 3 illustrating a schemeof reflector operation permitting regulation of the processing zonedimensions.

FIG. 5 illustrates the application of the output waveguide end facet asa reflector of particles.

FIG. 6 is a schematic representation of an embodiment of the inventionutilizing a vibrator for enhanced performance.

FIG. 7a is a schematic representation of an embodiment of this inventionwhich includes the additional application of spray and air-coolingsystems.

FIGS. 7b and 7 c are enlarged side and bottom views respectively of thetip for the embodiment shown in FIG. 7a.

FIGS. 8a and 8 b are schematic representations of two relatedembodiments of the invention which include a reflector of particles,where the output of the radiation delivery system is a mirror.

FIGS. 9a-9 c show embodiments of the inventions with a reflector ofparticles, where the output of the radiation delivery system is amicrolens.

FIGS. 10-12 illustrate three further embodiments of apparatus for use inpracticing the teachings of the invention.

DETAILED DESCRIPTION

The invention generally involves the recirculation of particlesresulting from the ablation of a solid, preferably hard material, theessence of the invention involving the following:

Under ablation, normally laser ablation, the processed material in manycases breaks up into small-sized particles. This is characteristic ofthe case where the destruction begins with the heating of a stronglyabsorptive center inside the material. In this case, the pressure of thestrongly heated up center results in the appearance of microcracks. Inthe paper “Human tooth in low and high intensive light fields” Proc.SPIE, v.2623, pp. 68-81, 1996 by G. Altshuler, this mechanism for thedestruction of enamel or dentin under the influence of Er:YAG laserradiation is described. The cracking of enamel or dentin occurs as aresult of the overheating of water inside the enamel's micropores ordentinal tubules. The products of ablation (particles) can be ejectedfrom a zone of destruction with very high speed. For example, during thedestruction of enamel by submillisecond pulses of Er:YAG laser, speedsfor ablation products of 300 m/s, with sizes for particles ofhydroxilapatite reaching 200 μm, have been measured. The most probableparticle size is approximately 20 μm. The kinetic energy of suchparticles can be 0.5 mJ, which is enough for the destruction of enameland dentin under collision.

During a laser pulse, the particles of processed material (for exampleenamel or dentin) being moved or deposited at an end facet of thewaveguide can be ablated and accelerated by the same pulse. Theparticles of enamel and dentin at the moment of contact with the endfacet of the waveguide can, due to strong absorption of light, blow upnear the surface of the waveguide causing damage to the waveguide whichresults in the emission of fast particles of waveguide material. Thesesecondary particles are accelerated by the laser radiation to increasethe volume of material in collision with the processed material.

When the laser pulse is terminated, the particles of processed material(for example, enamel or dentin), can deposit on the surface of adielectric, for example, the end facet of the waveguide. Therefore thenext pulse can ablate and accelerate these particles. As a result ofablation, they move towards a processing zone of the material intocollision with a surface of the processed material, resulting inadditional destruction. These deposited particles can also cause themicro destruction of the surface of the dielectric (waveguide) and theparticles of this dielectric destruction can be accelerated by the laserradiation in the direction of the processed material surface, causingadditional destruction thereof. A unit of suitable material may also bemounted between the waveguide/tip of the processing zone and may beablated by the laser to serve as an additional source of particles fordestruction of the processed material surface.

Thus, the recirculation of the particles described above results inincreased efficiency of processing, and this effect can be used forlaser processing of dielectric crystals, polymers, polycrystallinematerials, ceramics, composite materials and other hard materials. Whilethe invention disclosed herein is used mainly for hard dental tissues orother dental materials, the invention is not limited in any way to thisapplication and may be used for the materials indicated above andothers.

A schematic diagram of an experiment carried out to confirm the effectsof the recirculation of particles is shown in FIG. 1. The beam 1 ofEr:YAG laser radiation with a pulse energy of 0.3 mJ, pulse of duration0.3. ms, and beam diameter of 0.6 mm ablated the enamel 2 of a humantooth. The products of ablation 3 (hydroxilapatite particles) hit thesurface of a sapphire plate 4 positioned at an angle to the surface ofenamel 2. The hydroxilapatite particles 3, having a lower hardness thansapphire, were reflected from the surface of plate 4 back to the surfaceof enamel 2, but in a zone 6 displaced from laser crater 5. As a result,there were two craters on the surface of enamel 2; laser crater 5 andcrater 6 formed by the flow of fast enamel particles 3 reflected bysapphire plate reflector 4 (also see FIG. 2). The volume of crater 6formed by the particles 3 is approximately the same as that of lasercrater 5. Thus, particularly if there is overlapping of the craters, theefficiency of laser processing can be increased by at least a factor oftwo.

The layout of an embodiment of the invention for material processingbased on the effect of recirculation of particles is shown in FIGS. 3aand 3 b. The device consists of a laser 7, a radiation delivery systemshown as a light-guide 8 (for example, an optical fiber, hollow fiber,etc.), joined with an optical tip, shown as an output unit having awaveguide 9. A reflector 10 is located around waveguide 9. The outputunit can be replaceable and easily disconnected from housing 11 byscrew, bayonet or other conventional means. Waveguide 9 is made of atransparent material with a hardness which is preferably more than, butat least close to, the hardness of particles of the processed material,for example sapphire, quartz, glass, optical ceramics, and has afocusing or collimating surface on its leading edge. If reflector 10returns particles to a processing zone of material 12, they destroy thematerial and produce new particles which are redirected to theprocessing zone by the reflector. Thus, this process of circulation ofparticles can repeat many times, increasing the efficiency of theprocess. Therefore, the effect is a recirculation of particles.Reflector 10 is made of a hard material providing elastic reflection ofthe particles, for example diamond, sapphire, metal, ceramics,metaloceramics. To increase the life-time of waveguide 9 and reflector10, their surfaces facing processed material 12 can be covered with afilm of a hard material, for example diamond, sapphire etc. In thiscase, the hardness of waveguide material 9 and reflector 10 can be lowerthan the hardness of processed material 12.

The form of the reflector and its orientation are selected to direct theflow of particles to a selected zone on a surface of the processedmaterial. For example, the reflector surface can have the form of ahemisphere with a center concurrent with a focal point of radiation beam1 and located inside the material near the processed surface thereof. Inthis case, ejected particles 13 are reflected back, mainly to the zoneof laser ablation. If the center of the reflector orb 10 is displacedabove the surface of processed material 12, the reflected particles 14will hit on a surface of the processed zone mainly around the zone oflaser effect. In this case, the transversal size of the processed zonewill be enlarged (FIG. 4) (i.e., the damage zone for reflected particleswill be around that for laser effect resulting in an enlarged cavity).By changing the form of the reflecting surface (plane, ellipse,hyperboloid, cone, cylinder, etc.) and the layout of the reflector, itis possible to control the dimensions of the processed zone. Thereflection of particles is subject to the geometrical optics law;therefore the calculation for the optimization of the reflector issimilar to that for the design of an optical system. It should also benoted that the beam and the reflector can have an axis of a symmetry(round beam) or a plane of symmetry (knife cut).

An embodiment where the surface of the waveguide 9 functions as areflector is shown in FIG. 5. In this case, the surface may be plane(FIG. 5a), spherical (FIG. 5b), conic, cylindrical, etc.

An embodiment where the reflector 10 and the waveguide 9 are attached toa vibrator 15 is shown in FIG. 6. The vibrator provides movement in adirection either perpendicular or parallel to the surface of theprocessed material. It may also provide turning around an axis laying ina plane parallel to the plane of the processed surface as well movementsin this plane. The availability of these movements and turns allows theproducts of ablation to escape and thus not to be stored in the zonebetween the waveguide and reflector surfaces and the surface of material12. If these particles cannot escape, they hinder the reflection ofparticles. The effect of particle removal can be enhanced if themovement of the tip is synchronized with the laser pulses so that thetip is moving towards the surface of the processed material during theablation. Then the reflection of ablation products from the surface ofthe reflector increases their speed. The connection 16 providesair-tightness of the tip.

An embodiment where liquid or gas for cooling of processed material issupplied through channels 17, 18 to the zone of processing is shown inFIG. 7. The feeding of liquid or gas can take place between laser pulsesso the speed of particles will not be reduced. The liquid and/or gas canalso clean and protect the surface of the reflector and waveguideagainst the adhesion of particles. Underpressure/vacuum for the removalof the products of ablation may be supplied between pulses on the samechannels. If underpressure is used, the channels are preferably designedso that either particles are not drawn therein, or if drawn therein, arereturned. The underpressure also allows an increase in the speed of therecirculating particles because of decreased air resistance. Channels 17and 18 can be closely located to the treatment area so a dispersion ofparticles of liquid will be produced, providing uniform fluid depositionon a cooled surface, and also to achieving a spray-effect (evaporationof small-size drops). To provide for the removal of liquid and productsof ablation, small slits 19 can be made in the reflector. The removal ofexcess particles between pulses improves laser efficiency by as much asa factor of three. Channels 17 and 18 may have a spiral structure toprovide more effective cooling of waveguide 9 and reflector 10. Gas orliquid can also enter in the space between lightguide 8 and waveguide 9to cool their end facets.

For another embodiment, air is initially applied through a channel, forexample channel 17, to clean the area of processing, the tip, thereflector, and/or the space between the tip and area of processing. Afine water spray or mist is then applied through the other channel, thelaser/radiation source being fired during such misting. The mistingcools the area of processing and lasts for a sufficient time before theradiation source is fired to provide a thin (for example one to 100micron, preferably 10 micron) water coating on the area of processing,this water coating being ablated by the radiation to create a shock wavewhich can create microcracks in the material in the region ofprocessing, facilitating the generation of the particles. The water mistis not heavy enough to interfere with the movement of particles ofablation. After the radiation pulse, either the water mist or a strongerwater spray continues to be applied for a short period to cool and cleanthe area of processing. This sequence of operation may be repeated atthe repetition rate of the radiation source, for example one Hz to fiftyHz. While the three step processed indicated above (i.e., air before theradiation pulse, misting before and during the pulse and mist/sprayafter pulse) are preferably employed together, one or more of thesesteps may be employed independently for selected embodiments. It is alsopossible for the water spray to be continuous, preferably with varyingintensity, air for example being applied to the area of processingthrough the water mist.

FIG. 8a is a schematic diagram of an optical tip with a waveguide outputunit for an alternative embodiment. For this embodiment, waveguide 22can be hollow or filled with liquid. In both cases, the waveguide 22represents a cylindrical viahole (it can be a circular or ellipticalcylinder). The lateral surface of the hole is polished to mirror qualityor can be coated with a high-reflecting coating at the laser radiationwavelength. Radiation 21 from lightguide 8 of the radiation deliverysystem is directed to waveguide 22 by, for example, mirror 23. In orderto prevent contamination of the walls of waveguide 22, liquid or gas canbe passed through a hole as discussed above. The waveguide can be conic(FIG. 8b) where the concentration of radiation provided by the unit 23(mirror or lens) takes place on a small square of the processed material(i.e., there is a small spot size). The conic form of the waveguide isadjusted to the shape of the radiation beam extending from mirror 23 tomaterial 12, and the small size of the hole in the surface of reflector10 limits the undesirable penetration of ablation products to mirror 23,and at the same time provides the desirable large reflecting surface.

The layout of a tip with a microlens 24 as an output unit forconcentration of radiation on the surface of the processed material isshown in FIG. 9. This microlens may be an orb (FIG. 9a), hemisphere(FIG. 9c) or meniscus (FIG. 9b) and may be formed from sapphire or othersuitable material. The use of the microlens with plane, convex orconcave surface faced to the surface of the processed material increasesthe concentration of particles reflected from the surface of themicrolens. In order to reduce the effect of ablation particle adhesionto the surfaces of waveguide 9, microlens 24 and reflector 10, thesesurfaces can be coated with a material providing minimum adhesion withrespect to the material of the ablation particles.

As mentioned above, the effect of particle recirculation consists ofthree parts: the first one is the reflection of ablation products backto the crater being formed in the processed material; the second is theacceleration of particles deposited on the end facet surface ofwaveguide 9 or lens 24 and on reflector 10 into the crater; and third isthe acceleration of particles of material resulting from the ablation ordestruction of surfaces of the waveguide 9, lens 24 or reflector 10 bylaser radiation to the laser crater.

In all the versions of the devices shown in FIGS. 3-9, and in particularFIG. 5, two of these parts may play an essential role. In these devices,the reflector 10 and end facet of the waveguide 9 or lens 24 function asa repository for particles which have left the laser crater, but whichon reaching the waveguide, reflector or lens do not have sufficientenergy to be reflected, and therefore adhere to the surface. Theconstruction of a tip in which particles of ablated material can depositon the surfaces of waveguide 9 and reflector 10 is shown in FIG. 10.These surfaces thus simultaneously serve as a repository of theparticles. Such adhesion often occurs at the end of a pulse when energyis reduced.

Laser radiation passing through the surface of waveguide 9, for examplefrom the next pulse, and being reflected from the surface of thereflector 10, ablates the deposited particles of processed material,creating pressure which initiates particle movement towards the surfaceof processed material 12 where the particles cause additionaldestruction.

An embodiment where a third mechanism for producing recirculatingparticles is used is shown in FIG. 11. Radiation from light-guide 8 hitson a floppy film, fiber or other unit 25 of a composite material formedat least in part of a hard material such as sapphire particles. Unit 25can be an optical fiber made of a material which is partially orcompletely absorbed by the laser radiation, for example quartz, glass orsapphire, or a film coating of the same material. The width of unit 25can be less than that of the radiation so that, even if the unit isfully absorptive, radiation reaches the area of processing. Thus,radiation may reach the area of processing for this embodiment through aunit which is at least partially transparent and/or around the unit. Thelight-guide 8 and floppy unit 25 are fixed in a housing 26 which canfunction as a reflector. During each laser pulse, partial ablation ofthe material of the unit 25 from its surface facing the processedmaterial 12 takes place, this ablation accelerating the particles towardmaterial 12. Unit 25 should include a material having a hardness whichis at least close to and preferable more than the hardness of theprocessed material. Ablation of the material of unit 25 takes placebecause of absorption of laser radiation by its surface and/or due toabsorption of radiation by the products of ablation of the processedmaterial which are deposited on the surface of this unit. The particlesof material from unit 25 cause additional removal of processed material12. Since unit 25 can be damaged during each pulse, a system 27 isprovided for continuous or discrete moving of unit 25 between pulses.System 27 can, for example, be represented by a motor having an axis orshaft on which unit 25 can be reeled. If unit 25 is formed as acylindrical waveguide, it can also focus laser radiation on the surfaceof the processed material.

An embodiment having an output unit with a tip providing side processingof the material is shown in FIG. 12. In dentistry, such kind oftreatment is necessary, for example, for the processing of a toothbefore crown making. In this case, waveguide 9 is made with an edge cutangle “a” of 20°<a<60°. The waveguide is placed in reflector 10 with thereflecting surface parallel to the surface of processed material 12. Inthis case, low energy particles can adhere to a lateral area ofwaveguide 9 faced to the surface of material 12, and can be acceleratedto the surface of material 12 by the next laser pulse in the mannerpreviously described.

All the tips for the embodiments described above, when used in dentistryor certain other applications, can be made as one-time appliances,limited use appliances or extended use appliances, a softer tip beingused for a one-time tip, and the hardness of the tip increasing as theprojected use for the tip increases. In particular, in addition toobtaining particles from the processed material and/or from a unit 25 asshown in FIG. 11, particles may also be obtained from the tip. This canhappen in a number of ways. First, as indicated earlier, low energyparticles may adhere to the tip, particularly near the end of a lightpulse. Such particles may then be ablated and/or accelerated by the nextlaser/radiation pulse and can cause part of the tip to be removed withthem when ablated. Alternatively, particularly if a softer tip is used,high energy particles and ablating on the tip may cause particles tobreak off from the tip, which particles can be accelerated to thesurface of processed material 12. Similarly, reflector 10 may also beformed of a materials of varying hardness depending on the extent of usedesired for the reflector. The reflector may also serve as a source ofparticles based on mechanisms similar to those discussed above withrespect to the tip. Finally, depending on the material of the tip 9, theradiation passing through the tip may cause some ablation thereofresulting in additional particle production.

In order to realize the recirculation of particles, the radiationwavelength, pulse duration and energy density should be set withindefined ranges. The wavelength should be within the range of maximumabsorption of the processed material or a selected portion thereof. Thepulse duration should be of the same order or shorter than the time ofthermal relaxation of the absorbing fraction or layer of the processedmaterial with a thickness which is approximately the depth of lightpenetration in the material. The density of pulse energy should besufficient for destruction of the material by microexplosions. Theindicated parameters can be found for each processed material.Considering enamel, dentin and bone tissues, the wavelength of radiationshould correspond to wavelengths strongly absorbed by the maincomponents of hard tissues: water, hydroxilapatite and/or proteins. Therange of wavelengths should be 1.9-2.1 μm (water), 2.65-3.5 μm (water,hydroxilapatite, proteins), 5.6-7.5 μm (proteins), 8.5-11 μm (water,hydroxilapatite). Therefore, for example, holmium, erbium, CO and CO₂lasers can be used. The duration of pulses depends on the dimensions ofthe absorbing components—drops of water 0.01-10 μm, or water inside thedentinal tubules 1-10 μm, enamel prisms, interprismatic spaces 1-20 μm,collagen clusters 0.1-10 μm, and is normally within a 0.0001-1000 μsrange. The preferable range is 1-500 μs. Experiments show that theenergy density should be within the 0.5-500 J/cm² range (5-150 J/cm²range is preferable). An important parameter of the invention is thedistance S between the processed surface and the surface of thewaveguide 9. This distance should not be more than the length ofparticle flight during which the speed of the particle decreases by morethan a factor of ten. The decrease of speed takes place due to frictionof the particles moving in air; this decrease in particle speed can bereduced by providing reduced pressure or vacuum condition in the spacebetween the reflector/waveguide and the processed material. The distanceS can be determined according to the formula S=V₀/2γ(1−e^(−γ)), whereγ=18η/ρd², η=viscosity of air, ρ=density of particle material,d=particle diameter, V₀=initial speed of particles. Applying the formulafor hard tissues, S should be within the 0-10 mm range. The preferablerange is 0.1 mm.

Where the invention is being utilized for the removal of hard dentaltissues (for example, enamel, dentin, cement, and also tooth stains andfiling materials (including composites), laser 7 can be a lasergenerating radiation in the spectral range 2.69-3 μm. In particular, itmay be an Er:YAG laser or a laser based on Er:YSGG, Er:YLF, Er:YAP,Er:Cr:YAG or an ions Ho:KGd (WO₄)₂. CO₂ laser. The radiation from thelaser can be delivered to the tip via a solid waveguide, hollowwaveguide with a solid tip or via an optical system. The laser may beplaced directly inside a tip; the pumping radiation in this case can bethe radiation of another laser, for example a diode laser or solid-statelaser transmitted through the waveguide. The laser can also be made as awaveguide with a core doped by the ions, for example, of erbium. Opticalradiation sources other than lasers, for example flash lamps/arc lamps,may also be utilized in practicing the teachings of this invention inappropriate applications, particularly non-dental applications.

While the invention has been described above primarily with respect toembodiments for performing drilling or other processing on dental tissueand/or other dental materials, the invention is in no way limited tosuch applications and may, for example, be used in various orthopedicapplications for drilling or otherwise processing bone or other hardtissue or may be used in a wide variety of applications where solid,generally hard material such as metals, ceramic, glass, crystals,various composites certain plastics and the like are to be drilled orotherwise processed. Further, while the invention has been discussedwith respect to a number of preferred embodiments, and variations on theembodiments have also been discussed, it is to be understood that theseembodiments are for purposes of illustration only and that the inventionis to include the foregoing and other changes in form and detail whichmight be apparent to one skilled in the art and is to be limited only bythe following claims.

What is claimed is:
 1. A device for processing a hard solid material including: a source of pulsed radiation; at least one source of particles having a hardness which is at least close to that of said material; and a system for delivering radiation from said source to a region of processing of said solid material, said system system comprising a tip, including an end for delivering radiation, radiation accelerating particles from said at least one particle source, which particles are at least one of accelerated to and reflected to a region of processing on a surface of said solid material to influence the processing thereof.
 2. A device as claimed in claim 1 wherein said at least one particle source is said region of processing on the surface of said solid material, said radiation ablating said surface to create particles accelerated away from said surface, and said system including a reflector, at least some of said accelerating particles being reflected back to said region of processing by at least one of said tip and said reflector to further process said surface.
 3. A device as claimed in claim 2 wherein the radiation and the reflected at least some of said accelerating particles impinge on substantially a single point on said surface in said region of processing.
 4. A device as claimed in claim 2 wherein the radiation and the reflected at least some of said accelerating particles impinge on different points on said surface in said region of processing.
 5. A device as claimed in claim 2 wherein, at the end of at least some radiation pulses, some particles of ablation adhere to said tip, and wherein said adhered particles are an additional particle source for a subsequent radiation pulse, at least some of said adhered particles being ablated by said subsequent radiation pulse so as to be accelerated towards said region of processing.
 6. A device as claimed in claim 2 wherein said tip has an end facet shaped to function as a reflector for said accelerating particles.
 7. A device as claimed in claim 1 wherein at least a portion of said tip is ablated by said radiation, the ablated portion of said tip being a particle source for delivery to said region of processing.
 8. A device as claimed in claim 1 wherein said at least one source of particles includes a unit positioned between said tip and said region of processing, said unit being ablated by radiation applied thereto to produce particles of ablation directed to said region of processing.
 9. A device as claimed in claim 8 including a mechanism for advancing a portion of said unit between said tip and region of processing as the unit is ablated.
 10. A device as claimed in claim 1 wherein said source of pulsed radiation is a pulsed laser.
 11. A device as claimed in claim 1 wherein said particles have a hardness greater than that of said material in the region of processing.
 12. A device as claimed in claim 1 including a mechanism for facilitating the removal of said particles from an area between said tip and said region of processing between radiation pulses.
 13. A device as claimed in claim 12 including a mechanism which vibrates the tip.
 14. A device as claimed in claim 13 wherein vibration of the tip is synchronized with pulsed radiation from said source to enhance at least one of delivery of said particles delivery to the region of processing and the removal of said particles.
 15. A device as claimed in claim 12 wherein said mechanism for facilitating removal includes a mechanism for applying to said area at least one of a liquid, a gas and an underpressure to facilitate the removal of said particles.
 16. A device as claimed in claim 15 wherein said mechanism for applying is at least primarily operative between pulses from said source of pulsed radiation.
 17. A device as claimed in claim 1 wherein said tip is hollow, said radiation being directed therethrough to said region of processing.
 18. A device as claimed in claim 17 wherein said hollow tip is shaped to minimize entry of particles from said at least one particle source therein.
 19. A device as claimed in claim 1 wherein said tip has an end facet cut at an angle to facilitate side processing of the material.
 20. A device as claimed in claim 19 wherein said angle is 20° to 60°.
 21. A device as claimed in claim 1 wherein the radiation from said source is of a wavelength preferentially absorbed by said solid material.
 22. A device as claimed in claim 21 wherein radiation from said source has a pulse duration which is of the same order or shorter than the thermal relaxation time of an absorbing fraction of said solid material.
 23. A device as claimed in claim 1 wherein a distance between the end of said tip and a surface of said material to be processed is not more than a distance of flight of said particles during which particle speed decreases by a factor of ten.
 24. A device as claimed in claim 1 wherein said tip includes a dielectric waveguide with a facet which is one of plane, conic, cylindrical and spherical.
 25. A device as claimed in claim 1 wherein said tip end includes a microlens.
 26. A device as claimed in claim 1 wherein said tip includes a portion focusing said radiation at or below a surface of said region of processing.
 27. A device as claimed in claim 1 including a mechanism for applying at least one of a liquid and a gas to cool said region of processing.
 28. A device as claimed in claim 1 including a reflector surrounding the end of the tip and said reflector shaped to direct the particles to said region of processing and to control dimensions of said region.
 29. A device as claimed in claim 1 including a mechanism applying a fine water spray or mist to said region of processing during radiation pulses from said source.
 30. A device as claimed in claim 29 wherein said mechanism also applies said fine water spray or mist for a period prior to each radiation pulse sufficient for a thin coating of water to form on said region of processing.
 31. A device as claimed in claim 29 including a mechanism for applying air to said region of processing prior to each radiation pulse.
 32. A device as claimed in claim 29 including a mechanism for applying a water spray to said region of processing after each radiation pulse.
 33. A device as claimed in claim 1 wherein said solid material is at least one of dental enamel, dentin, bone, other dental tissue, filling material, cementum and stain.
 34. A device for processing dental material including at least one of dental enamel, dentin, bone, other dental tissue, filling material, cementum and stain, comprising: a source of pulsed radiation at a wavelength preferentially absorbed by the dental material; a source of particles which has a hardness which is at least close to that of said dental material in a region of processing; and a system delivering radiation from said source of pulsed radiation to a region of processing on a surface of said dental material to at least partially influence the processing thereof, radiation also being delivered to said source of particles to accelerate particles therefrom, said particles being at least one of accelerated to and reflected to the region of processing to further influence said processing.
 35. A device as claimed in claim 34 wherein said particle source is said region of processing on the surface of said dental material, said radiation ablating said surface to create particles accelerated away from said surface, at least some of said accelerating particles are reflected back to a region of processing by at least one of said tip for delivering radiation on said system and reflector to further process said surface.
 36. A device as claimed in claim 35 wherein, at the end of at least some radiation pulses, some particles of ablation adhere to said tip, and wherein said adhered particles are an additional particle source for a subsequent radiation pulse, at least some of said adhered particles being ablated by said subsequent radiation pulse so as to be accelerated towards said region of processing.
 37. A device as claimed in claim 35 wherein at least a portion of said tip ablated by said radiation, the ablated portion of said tip being a particle source for delivery to said region of processing.
 38. A device as claimed in claim 35 wherein said source of particles includes a unit positioned between said tip and said region of processing, said unit being ablated by radiation applied thereto to produce particles of ablation directed to said region of processing.
 39. A device as claimed in claim 35 including a mechanism for facilitating the removal of said particles from an area between said tip and said region of processing between radiation pulses.
 40. A device as claimed in claim 35 wherein said tip has an end facet cut at an angle to facilitate side processing of the dental material.
 41. A device as claimed in claim 40 wherein said angle 20° to 60°.
 42. A device as claimed in claim 34 wherein said source of pulsed radiation is a pulsed laser.
 43. A device as claimed in claim 42 wherein the pulsed laser is one of Er:YAG with a wavelength of 2.94 μm, Er:YLF with a wavelength in the 2.71-2.87 μm range, Er:YGG with a wavelength of 2.7-2.8 μm, CTE:YAG with a wavelength in the 2.65-2.7 μm range, Ho:KGd(WO₄)₂ with a wavelength of 2.93 μm, and CO₂ with a wavelength in the 9-11 μm range.
 44. A device as claimed in claim 34 including a mechanism for cooling said dental material.
 45. A method of processing dental material including at least one of dental enamel, dentin, bone, other dental tissue, filling material, cementum and stain, comprising: exposing the dental material to pulsed radiation to influence the processing thereof in a region of processing; utilizing the pulse radiation to generate particles of ablation; and reflecting directing said particles of ablation to said region of processing of the dental material to further influence processing thereof.
 46. A method as claimed in claim 45 wherein said pulsed radiation is of an energy above an ablation threshold for the dental material.
 47. A method as claimed in claim 46 wherein some particles of ablation are deposited on a surface adjacent said region of processing.
 48. A method as claimed in claim 45 including at least one of a tip and an extra piece of material through said radiation passes and which is partially abated during said utilizing step to generate additional particles reflected during said reflecting step to said region of processing.
 49. A method as claimed in claim 45 wherein said pulsed radiation is from a laser with a wavelength within one of 1.91-2.1 μm, 2.65-3.5 μm, 5.6-7.5 μm, and 8.5-11 μm; a duration of 0.0001-10000 μs; and an energy density of 0.5-500 J/cm².
 50. A method as claimed in claim 45 including at least one of cooling the region of processing of said dental material and removing said particles from an area between a source of said pulsed radiation and said region of processing between pulses of said radiation.
 51. A method as claimed in claim 45 including directing a fine water spray or mist at said region of processing during each pulse of said radiation.
 52. A method as claimed in claim 51 wherein said directing a fine water spray or mist step lasts for a sufficient period prior to each radiation pulse for a thin water coating to be formed on said region of processing.
 53. A method as claimed in claim 45 including at least one of directing air at said region of processing before each pulse of said radiation and directing a water spray to said region of processing after each said pulse. 